Method of construction of a balloon catheter

ABSTRACT

The method of manufacturing a polyurethane balloon catheter from a length of tubing of such material wherein the tubing is placed in a mold of the desired final expanded shape, the mold and tubing are immersed in a bath of warm water, and air pressure is introduced into the tubing to effect the expansion and then withdrawn to allow the removal of the balloon.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of Ser. No. 07/979,248filed Nov. 11, 1992 now U.S. Pat. No. 5,370,618.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention resides in the field of pulmonary artery balloon cathetersand more particularly relates to low inflation pressure, low deflatedprofile, self centering polyurethane devices.

2. Description of the Prior Art

Pulmonary artery balloon catheters for measuring pressures within thevascular system are well known devices in the medical field. Theirprimary purpose is, after insertion into the body of the patient, toprovide a means for performing such measurements by inflating theballoon attached to the catheter tip. This is accomplished, for example,by the introduction of fluid into the balloon through the catheter by asyringe located externally to the patient. These catheters are intendedto be left within the body for an extended period of time and thereforetheir construction as well as their maneuverability, manipulation, andactivation with minimum danger to the patient are of great concern.

The primary material for manufacturing these balloons heretofore hasbeen latex. There are a number of drawbacks to the use of latex whichare alleviated entirely or in part by the employment of polyurethane inaccordance with applicants invention. Among these drawbacks are thefollowing.

Inflation of latex balloons is erratic due to the high tension of thematerial compared to polyurethane. This results in a surge to full sizewhen the critical inflation pressure is reached as well as a tendency toinflate non uniformly or out of round nearest the catheter inflationport.

As a natural material, latex varies from lot to lot, decomposes orspoils easily and is difficult to extrude with even wall thickness.

Mechanically, it is not as durable as polyurethane, fragments when itbursts, diffuses filling gases quickly and absorbs bodily fluids.Further latex has a rougher surface making balloons composed of thatmaterial more difficult to introduce into the body and more likely topromote blood clots upon long periods of in-dwell.

Additionally latex has undesirable toxins and pollutants from its sourceand processing and can cause severe allergic reactions in some patients.

Finally it is not as easily mounted on a catheter requiring adhesivesand metal bands which may be avoided with polyurethane by usingsolvents.

The use of polyurethane as a catheter balloon material has however beendisclosed in the prior art. For example U.S. Pat. No. 4,913,701 Tower,describes a polyethylene catheter employing a thermoset polyurethaneballoon attached by cuffs and an appropriate adhesive. The referencescontained therein particularly U.S. Pat. No. 4,661,095, Taller et al.further disclose various aspects of the technology involved in thisendeavor.

Applicant has now discovered that by constructing such catheters andballoons of a particular material in a particular way, a superior devicecan be created which overcomes many of the deficiencies of thosecomprised of latex and those comprised of polyurethane as has beenpreviously disclosed.

SUMMARY OF THE INVENTION

The invention may be summarized as a low deflated profile, low inflationpressure, self centering polyurethane balloon catheter. The balloon iscomprised of substantially 80A durometer 0.004 inch wall thicknessmaterial and is preferably formed by blow molding in a bell shaped moldto achieve a device of particular elasticity which behaves uponinflation and deflation in a specific and desirable manner.

In contrast to the prior art, the catheter balloon of the inventionobtained by the unique method of manufacturing disclosed herein providesa number of features and advantages constituting a significant advancein the field of pulmonary artery pressure measurements. For example thedesign and method of construction of the balloon provides a catheterwhich self centers in the artery under blood flow upon inflation. Thisresults from an initial low inflation pressure characteristic whichfills the balloon uniformly to an unstretched state followed by anadditional application of inflation pressure which expands and stretchesthe balloon to the desired diameter and shape. Additionally the designand method of construction produce a rapidly obtained low deflatedprofile upon the release of inflation pressure without the necessity ofdrawing a vacuum, a result of the inherent elastic memory of the device.Further, by the use of a solvent to smoothly join the catheter andballoon rather than the mechanical or adhesive bonds of previousdevices, the opportunity for blood clotting is greatly reduced. This isa particularly desirable aspect of the invention as these types ofcatheters normally dwell within the patient for a number of days.

Additional features which enhance the effectiveness and reliability ofthe invention include the use of epoxy for balloon-catheter jointreinforcement, and the arrangement of the balloon to cover the cathetertip when deflated.

The balloon is preferably made by introducing extruded 70A to 95Adurometer polyurethane tubing into a clear acrylic or glass mold with abell shaped cavity. The mold is dipped into hot water, and stabilized atabout 165 degrees F. for about 35 seconds. One end of the tubing whichis in the mold is plugged. The other end of the tubing which is outsideof the mold is attached to a syringe. When the mold has been in the hotwater for the required time, pressure is exerted into the tubing byadvancing the plunger of the syringe filled with air. The tubing expandsdue to the air pressure to fill the shape of the cavity. The action ofthe tubing expanding to fill the cavity can be visually seen through theclear walls of the mold. When formation of the balloon is finished, theclear balloon material most often turns white for a second and then backto clear.

The mold is pulled from the hot water and dipped into cold waterpreferably within about two seconds of witnessing the extruded materialfilling the cavity. The plunger of the syringe is withdrawn collapsingthe balloon allowing removal from the mold. Excess tubing material istrimmed and the proximal end of the balloon attached to the catheter byan appropriate solvent. The distal end is then everted over or reversedonto the catheter shaft below the proximal end and again attached withsolvent complete the integration of the balloon and catheter. Evertingprovides a means for the balloon to cover the catheter tip on deflation.It is not necessary to obtain the other characteristics of theinvention.

The above described features and advantages of the invention will bemore clearly understood from the description of the preferred embodimentand the accompanying drawings which follow.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of the balloon in the inflated statewhich comprises the preferred embodiment of the invention;

FIG. 1a is a cross sectional view of the balloon of FIG. 1 in thedeflated state; and

FIG. 2 is a cross sectional view of a mold used to construct thepreferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, there is illustrated a catheter balloon in theinflated state comprising the preferred embodiment of the invention.Balloon 10 comprised of 70A to 95A durometer polyurethane of 0.004 inchwall thickness is disposed in neck section 12 formed at the distal endof polyurethane catheter 14. It is attached so as to be fluid tight atsections 16 and 18 and is preferably secured by the application of asolvent, cylcohexanone for example. Inflation and deflation isaccomplished by the introduction or withdrawal of fluid at the proximalend 20 of catheter 14 connecting with port 22 in the catheter wall. Asshown in FIG. 1, balloon 10 extends at its greatest inflated distalextremity beyond neck section 12. Pressure is measured through thecatheter by way of tip port 24 which is separated from the ballooninflation channels by a multi lumen interior structure not shown but asis well known to those skilled in the art. Catheter--balloon interfaces16 and 18 may further be reinforced by the application of rings of epoxy26 and 28 which serves to streamline the surface reducing the risk ofblood clots and facilitating the introduction and removal of the entiredevice into the cardiovascular system of the patient. For the samepurpose, the balloon is also mounted in a manner to provide for the tipof the catheter to be covered upon deflation as shown in FIG. 1a.

The specified elasticity (durometer) and wall thickness of thepolyurethane directly result in the features and advantages of theinvention described above. Although the balloon may be constructed invarious ways a preferred method of construction as will be describedbelow utilizing a mold has been found to yield a superior andreproducable device.

Referring to FIG. 2, there is shown a cross sectional view of a moldparticularly suited for the manufacture of the invention. Mold 30 ispreferably composed of a clear material such a glass or acrylic.

It is cylindrical having a central portion 32 of greater diameter thaneach end portion and as shown such portion may be described as bellshaped, that is, the cross sectional slope 34 of the forward part 36 isless steep than cross sectional slope 38 of the rearward portion 40.

Forward part 36 provides an end seal 42 and for that purpose isinternally tapered to produce a wedge fit upon the insertion of apolyurethane tubing work piece 44. Holes 46 provide for the escape ofair when the mold is filled by the expanding workpiece.

A preferred method of construction of the balloon and cathetercomprising the invention using the above described mold is as follows:

Extruded 80A durometer semi-elastic polyether, segrented, thermoplasticpolyurethane tubing with a wall thickness of about 0.004" and an insidediameter appropriate to fit tightly over a catheter shaft is insertedinto a glass mold with a bell shaped bulb in the center as is describedabove and is 15 percent smaller in diameter than the intended finalinflated balloon size i.e. 10-13 mm. The bell shape of the mold isadvantageous to reduce the amount of excess balloon material to providethe lowest deflated profile. The upper half of the mold is cylindricalin shape with a hole in the center with an inner diameter just largeenough to freely accept the introduction of the polyurethane tubing. Thebottom half of the mold is tapered so that the polyurethane tubing maybe friction fitted and sealed at the bottom portion of the mold which isclosed at the end. The polyurethane tubing is attached to a rigid tubewith a diameter 20 percent larger than the polyurethane tubing bystretching the tubing over the rigid tube and melting or solvent bondingthe polyurethane tubing to the rigid tube so that a seal is formed. Theother side of the rigid tube has a luer lock connector so that a syringewith a pressure gauge may be attached. The syringe should have a volumeat least equal to that of the intended end balloon inflation volume.After the syringe is attached to the rigid tube and the polyurethanetubing to the glass bulb mold and a seal is verified, the bell shapedglass bulb is immersed in a temperature controlled water bath of about160 degrees F. to 168 degrees F. The mold is immersed just past the bulbin the mold. The bulb is left in the hot water for about 30 to 35seconds, after which the syringe plunger is gradually advanced to expandthe tubing. While pressure is increased with the syringe the tubing isconstantly pulled back in a gentle manner. This removes slack from thetubing which when the tubing blows to fill the mold, would be pulledinto the bulb and otherwise cause a mis-formed balloon. During about thelast 10 percent of the depression of the syringe the polyurethane tubingwill expand to fill the shape of the glass bulb. After the tubing isblown into the shape of the bulb more pressure is exerted to completelyfill the corners of the mold and set the balloon shape. The mold isremoved from the hot water bath and set in a cold water bath of about 40degrees F. while the balloon is still inflated. After about 5 seconds,the syringe plunger is withdrawn to pull the tubing off the walls of thebulb and to pull the rigid tube away from the mold to remove thepolyurethane tubing including the blown balloon bulb center from themold. The bottom portion of the polyurethane tubing is pinched with ahemostat for example to seal the end and to allow inflation of theballoon in the air to test for symmetry and shape.

Unexpanded portions of tubing above and below balloon are cut, allowinga 2 mm section on each end for mounting purposes. The polyurethanematerial catheter is prepared by tapering the tip in two parts using aheated mold. The first taper, just long enough to accomodate the portionof the tubing to be bonded to the catheter, about 2 mm, is greater thanthe second longer taper, about 7 mm. The bottom portion of the balloonis then mounted on the top taper of the catheter by stretching thetubing of the balloon into place over the extra tapered 2 mm segment.When in place the solvent cylcohexanone is wiped onto the 2 mm segmentusing an ordinary nylon paint brush, avoiding contact with the blownballoon itself. A pair of heated crimping pliers may be used to crimpseal the 2 mm segment onto the catheter in addition to the chemicalbonding. The balloon-catheter is then set aside for about 10 minutes toallow the chemical bond reaction created by the cylcohexanone. Afterthis, the balloon is flipped over itself or everted creating a cone overthe catheter tip and setting in place the second 2 mm segment of balloontubing to be mounted onto the bottom portion of the polyurethanecatheter tip tapered portion. This segment is bonded as the first bypainting cyclohexanone on the segment to create a chemical bond betweenthe polyurethane balloon tubing segment and the polyurethane cathetertapered portion. Again, a pair of heated crimping pliers may be used toreinforce the strength of the bond by melting the balloon tubing segmentinto the polyurethane catheter material. After allowing this segment toset for 10 minutes, epoxy bands are painted for exampleIsoproplidenediphenol epichlorohyrin based epoxy and/or similar isomersaround the sections of the balloon tubing that were chemically bonded tothe catheter. This serves the purpose of smoothing out the transition ofthe balloon to the catheter to reduce the chance of causing a stagnationpoint in the flow of blood. It also serves a second purpose ofreinforcing the balloon to catheter bond and smoothing out the tipportion of the catheter to avoid scraping the inside of the blood vesselwalls.

What is claimed is:
 1. The method of manufacturing a balloon cathetercomprising the steps of(a.) providing a cylindrical mold having acentral portion of greater diameter than each end portion; (b.)providing a length of substantially 80A durometer polyurethane tubinghaving a wall thickness of substantially 0.004 inches; (c.) insertingsaid tubing into said mold; (d.) closing one end of said tubing; (e.)immersing said mold and said tubing in a bath of warm water of aselected temperature for a selected time; (f.) introducing pressurizedair into said tubing to expand said tubing into said mold to create aballoon; (g.) immersing said mold and said tubing in a bath of coldwater of a selected temperature for a selected time; (h.) withdrawingsaid air pressure to produce a vacuum to collapse said balloon; (i.)withdrawing said balloon from said mold; (j.) providing a cathetercomprising a length of polyurethane tubing; (k.) producing a fluid portin the wall of said catheter at one end; (l.) placing one end of saidballoon above said port and bonding said end with a solvent to saidcatheter to form a bonded juncture and everting the opposite end of saidballoon over said end and bonding said opposite end to said catheterbelow said port to form another bonded juncture and thereby enclose saidport; and (m.) disposing a ring of epoxy on each of the bonded juncturesof said balloon and said catheter.
 2. The method of claim 1 wherein saidsolvent comprises cylcohexanone.
 3. The method of claim 1 wherein saidpressurized air is introduced into said tubing by the use of a syringe.4. The method of claim 1 wherein said central portion of said mold isbell shaped.
 5. The method of claim 1 wherein said selected temperaturein step (e.) is about 160 to 168 degrees F. and said selected time instep (e.) is about 30 to 35 seconds.
 6. The method of claim 1 furtherincluding the step of heat sealing said catheter and said balloon at thebonded junctures of said balloon and said catheter.